Reconstruction of the proximal ends of retiolitid rhabdosomes (Graptolithina) from the Upper Wenlock and the Lower Ludlow

Detailed study of the ultrastructures on the cortical lists of retiolitids occurring after the lundgreni event has been undertaken. The extremely well preserved material from the Go?dap borehole of Poland (Baltica) enables classification of clathrial lists into two types—with single and double seams. Significantly different seam development is observed between two groups of retiolitids occurring before and after the lundgreni event. The study of seams and increments on the lists enables reconstruction of the membrane arrangement of the rhabdosomes. Reconstruction of the proximal ends, the arrangement of the ancora umbrella, and the layout of the proximal ventral and lateral orifices of five genera, Neogothograptus, Holoretiolites, Plectograptus, Spinograptus, and Quattuorgraptus n. gen., is presented. The new genus Quattuorgraptus is separated from Spinograptus because of the different development of the ancora umbrella and the width of the lateral walls of the rhabdosome.     

Effect of Metalaxyl on the incidence and severity of Pearl millet downy mildew disease in Northern Nigeria

Pearl millet downy mildew (DM) incidence, severity and yield losses of two pearl millet varieties (local and improved) due to the disease were determined in the field. Significant differences in the disease incidence and severity were recorded in the plots sown with metalaxyl-treated seeds and those sown with non-treated seeds, indicating the efficacy of the fungicide on the fungus. Yield losses due to non-treatment of seeds with metalaxyl was 40.88 and 45.39% in a local variety and 43.00 and 18.60% in an improved variety in the 2000 and 2001 cropping seasons respectively. Significant differences between plots sown with metalaxyl-treated and those sown with non-treated seeds were obtained for other yield components such as 1000-grains weight, panicle length and weight.     

Gene expression and the evolution of phenotypic diversity in social wasps

Background  

Organisms are capable of developing different phenotypes by altering the genes they express. This phenotypic plasticity provides a means for species to respond effectively to environmental conditions. One of the most dramatic examples of phenotypic plasticity occurs in the highly social hymenopteran insects (ants, social bees, and social wasps), where distinct castes and sexes all arise from the same genes. To elucidate how variation in patterns of gene expression affects phenotypic variation, we conducted a study to simultaneously address the influence of developmental stage, sex, and caste on patterns of gene expression in Vespula wasps. Furthermore, we compared the patterns found in this species to those found in other taxa in order to investigate how variation in gene expression leads to phenotypic evolution.     

Biochemical characterization of the tobacco 42-kD protein kinase activated by osmotic stress

In tobacco (Nicotiana tabacum), hyperosmotic stress induces rapid activation of a 42-kD protein kinase, referred to as Nicotiana tabacum osmotic stress-activated protein kinase (NtOSAK). cDNA encoding the kinase was cloned and, based on the predicted amino acid sequence, the enzyme was assigned to the SNF1-related protein kinase type 2 (SnRK2) family. The identity of the enzyme was confirmed by immunoprecipitation of the active kinase from tobacco cells subjected to osmotic stress using antibodies raised against a peptide corresponding to the C-terminal sequence of the kinase predicted from the cloned cDNA. A detailed biochemical characterization of NtOSAK purified from stressed tobacco cells was performed. Our results show that NtOSAK is a calcium-independent Ser/Thr protein kinase. The sequence of putative phosphorylation sites recognized by NtOSAK, predicted by the computer program PREDIKIN, resembled the substrate consensus sequence defined for animal and yeast (Saccharomyces cerevisiae) AMPK/SNF1 kinases. Our experimental data confirmed these results, as various targets for AMPK/SNF1 kinases were also efficiently phosphorylated by NtOSAK. A range of protein kinase inhibitors was tested as potential modulators of NtOSAK, but only staurosporine, a rather nonspecific protein kinase inhibitor, was found to abolish the enzyme activity. In phosphorylation reactions, NtOSAK exhibited a preference for Mg(2+) over Mn(2+) ions and an inability to use GTP instead of ATP as a phosphate donor. The enzyme activity was not modulated by 5'-AMP. To our knowledge, these results represent the first detailed biochemical characterization of a kinase of the SnRK2 family.     

A novel splicing variant encoding putative catalytic α subunit of maize protein kinase CK2

A cDNA highly homologous to the known catalytic α subunit of protein kinase CK2 was cloned from maize ( Zea mays ). It was designated ZmCK 2α-4 (accession no. AAF76187). Sequence analysis shows that ZmCK2α-4 and the previously identified ZmCK2α-1 (accession no. X61387) are transcribed from the same gene, ZmPKCK2AL (accession no. Y11649), but at different levels in various maize organs and at different stages of development. The cDNA encoding ZmCK2α-4 has three potential translation initiation sites. The three putative variants of ZmCK2α-4 were expressed in Escherichia coli as GST-fusion proteins and purified from bacterial extracts. In contrast to the previously characterized ZmCK2αs, the obtained GST:ZmCK2α-4 proteins were catalytically inactive as monomers or in the presence of equimolar amounts of the human CK2β. However, GST:ZmCK2α-4 did phosphorylate casein in the presence of a large excess of the β subunit. The activity of ZmCK2α-4 toward casein could also be stimulated by increasing ATP concentration. Modeling studies have shown that there is no interaction between the N-terminal segment of ZmCK2α-4 and the activation loop responsible for constitutive catalytic activity of CK2α. Preliminary results suggest that ZmCK2α-4 may function as a negative regulator of other CK2s, and at certain circumstances as a holoenzyme which catalytic activity is stimulated by specific regulatory subunit(s).     

SNF1-Related Protein Kinases Type 2 Are Involved in Plant Responses to Cadmium Stress

Cadmium ions are notorious environmental pollutants. To adapt to cadmium-induced deleterious effects plants have developed sophisticated defense mechanisms. However, the signaling pathways underlying the plant response to cadmium are still elusive. Our data demonstrate that SnRK2s (for SNF1-related protein kinase2) are transiently activated during cadmium exposure and are involved in the regulation of plant response to this stress. Analysis of tobacco (Nicotiana tabacum) Osmotic Stress-Activated Protein Kinase activity in tobacco Bright Yellow 2 cells indicates that reactive oxygen species (ROS) and nitric oxide, produced mainly via an l-arginine-dependent process, contribute to the kinase activation in response to cadmium. SnRK2.4 is the closest homolog of tobacco Osmotic Stress-Activated Protein Kinase in Arabidopsis (Arabidopsis thaliana). Comparative analysis of seedling growth of snrk2.4 knockout mutants versus wild-type Arabidopsis suggests that SnRK2.4 is involved in the inhibition of root growth triggered by cadmium; the mutants were more tolerant to the stress. Measurements of the level of three major species of phytochelatins (PCs) in roots of plants exposed to Cd²⁺ showed a similar (PC2, PC4) or lower (PC3) concentration in snrk2.4 mutants in comparison to wild-type plants. These results indicate that the enhanced tolerance of the mutants does not result from a difference in the PCs level. Additionally, we have analyzed ROS accumulation in roots subjected to Cd²⁺ treatment. Our data show significantly lower Cd²⁺-induced ROS accumulation in the mutants’ roots. Concluding, the obtained results indicate that SnRK2s play a role in the regulation of plant tolerance to cadmium, most probably by controlling ROS accumulation triggered by cadmium ions.Cadmium is one of the most toxic soil pollutants. Cadmium ions accumulate in plants and affect, via the food chain, animal and human health. In plants, cadmium is taken up by roots and is transported to aerial organs, leading to chromosomal aberrations, growth reduction, and inhibition of photosynthesis, transpiration, nitrogen metabolism, nutrient and water uptake, eventually causing plant death (for review, see DalCorso et al., 2008). Plants are challenged not only by cadmium ions themselves, but also by Cd²⁺-induced harmful effects including oxidative stress (Schützendübel et al., 2001; Olmos et al., 2003; Cho and Seo, 2005; Sharma and Dietz, 2009). The extent of the detrimental effects on plant growth and metabolism depends on the level of cadmium ions present in the surrounding environment and on the plant’s sensitivity to heavy metal stress.Tolerant plants avoid heavy metal uptake and/or induce the expression of genes encoding products involved, directly or indirectly, in heavy metal binding and removal from potentially sensitive sites, by sequestration or efflux (Clemens, 2006). The best-characterized heavy metal binding ligands in plants are thiol-containing compounds metallothioneins and phytochelatins (PCs), whose production is stimulated by Cd²⁺. PCs bind metal ions and transport them to the vacuole, thus reducing the toxicity of the metal in the cytosol (for review, see Cobbett, 2000; Cobbett and Goldsbrough, 2002). PCs are synthesized from reduced glutathione (GSH). Therefore, production of compounds involved in cadmium detoxification and, at the same time, in cadmium tolerance closely depends on sulfur metabolism. So far, our knowledge on the cellular processes induced by cadmium that lead to changes in sulfur metabolism in plants has been rather limited.Protein kinases and phosphatases are considered major signal transduction elements. However, until now only a few of them have been described to be involved in cadmium stress response or sulfur metabolism. For instance, excessive amounts of cadmium or copper activate mitogen-activated protein kinases (MAPKs) in Medicago sativa (Jonak et al., 2004), rice (Oryza sativa; Yeh et al., 2007), and Arabidopsis (Arabidopsis thaliana; Liu et al., 2010). Studies on rice MAPKs involved in heavy metal stress response indicate that the activity of these kinases depends on the oxidative stress induced by Cd²⁺. Moreover, Yeh et al. (2007) suggested that the activation of MAPKs in rice by cadmium or copper required the activity of calcium-dependent protein kinase (CDPK) and PI3 kinase, since the MAPK pathways involved in cadmium and copper stress response could be inhibited by a CDPK antagonist (W7) or a PI3 kinase inhibitor (wortmannin). However, so far the function of the identified kinases in plant adaptation to heavy metal pollution has not been established. There is some information concerning an involvement of CDPK in sulfur metabolism (Liu et al., 2006). Soybean (Glycine max) Ser acetyltransferase (GmSerat2;1), the enzyme that catalyzes the first reaction in the biosynthesis of Cys from Ser, is phosphorylated by CDPK. The phosphorylation has no effect on GmSerat2;1 activity, but it renders the enzyme insensitive to the feedback inhibition by Cys (Liu et al., 2006). There is growing evidence that SnRK2s (for SNF1-related protein kinase2) play a role in the regulation of sulfur metabolism. Most information showing a connection between SnRK2s and sulfur metabolism comes from experiments on the lower plant Chlamydomonas reinhardtii (Davies et al., 1999; Irihimovitch and Stern, 2006; González-Ballester et al., 2008, 2010). SNRK2.1 is considered a general regulator of S-responsive gene expression in C. reinhardtii (González-Ballester et al., 2008).In higher plants the SnRK2 family members are known to be involved in plant response to drought, salinity, and in abscisic acid (ABA)-dependent plant development (Boudsocq and Laurière, 2005; Fujii et al., 2007, 2011; Fujii and Zhu, 2009; Fujita et al., 2009; Nakashima et al., 2009; Kulik et al., 2011). Ten members of the SnRK2 family have been identified in Arabidopsis and in rice (Boudsocq et al., 2004; Kobayashi et al., 2004). All of them, except SnRK2.9 from Arabidopsis, are rapidly activated by treatment with different osmolytes, such as Suc, mannitol, sorbitol, and NaCl, and some of them also by ABA. Results presented by Kimura et al. (2006) suggest that in Arabidopsis, similarly to C. reinhardtii, some SnRK2s are involved in the regulation of S-responsive gene expression and O-acetyl-l-Ser accumulation under limited sulfur supply, indicating that also higher plants’ SnRK2s could be involved in sulfur metabolism.As it was mentioned before, oxidative stress induced by cadmium ions significantly contributes to the metal toxicity. Reactive oxygen species (ROS) can be produced in many different reactions in various compartments of the cell in response to cadmium (Romero-Puertas et al., 2004; Heyno et al., 2008; Tamás et al., 2009). The best-characterized ROS-generating enzymes that take part in the response to cadmium are the plasma-membrane-bound NADPH oxidases (Olmos et al., 2003; Romero-Puertas et al., 2004; Garnier et al., 2006). There are some indications that plant NADPH oxidases are phosphorylated by SnRK2s (Sirichandra et al., 2009), therefore it is highly plausible that SnRK2s play a role in the regulation of ROS accumulation in plants subjected to cadmium stress. Taking into consideration all facts mentioned above we hypothesized that SnRK2s could be involved in the plant response to stress induced by cadmium ions. To verify this conjecture, we analyzed the activity and potential role of selected SnRK2s, in tobacco (Nicotiana tabacum) cells and Arabidopsis plants, in the response to cadmium ions.     

Nitric oxide signalling in plants: interplays with Ca2+ and protein kinases

Much attention has been paid to nitric oxide (NO) research since its discovery as a physiological mediator of plant defence responses. In recent years, newer roles have been attributed to NO, ranging from root development to stomatal closure. The molecular mechanisms underlying NO action in plants are just begun to emerge. The currently available data illustrate that NO can directly influence the activity of target proteins through nitrosylation and has the capacity to act as a Ca2+-mobilizing intracellular messenger. The interplay between NO and Ca2+ has important functional implications, expanding and enriching the possibilities for modulating transduction processes. Furthermore, protein kinases regulated through NO-dependent mechanisms are being discovered, offering fresh perspective on processes such as stress tolerance.